The central goal of this investigation is to use diploid human fibroblasts to examine the relationships between cell surface proteins and cellular senescence. Fibroblasts from aged donors, donors with syndromes of premature senescence, and in vitro age cells will be used. Surface proteins will be extracted from cell membranes and from conditioned media and prepared by gel filtration and analyzed by gel electrophoresis. In addition, the presence or absence of specific membrane features will be detected by lectin binding and agglutination and by producing antiserum that is specific for post-replicative cell membranes.